Symmetrical Pole Placement Method-Based Unity Proportional Gain Resonant and Gain Scheduled Proportional (PR-P) Controller With Harmonic Compensator for Single Phase Grid-Connected PV Inverters

ABSTRACT:

In this paper, a symmetrical pole placement Method-based Unity Proportional Gain Resonant and Gain Scheduled Proportional (PR-P) Controller is presented. The proposed PR-P controller resolved the issues that are tracking repeating control input signal with zero steady-state and mitigating of 3^rd order harmonic component injected into the grid associated with the use of PI controller for single-phase PV systems. Additionally, the PR-P controller has overcome the drawbacks of frequency detuning in the grid and increase in the magnitude of odd number harmonics in the system that constitute the common concerns in the implementation of conventional PR controller developed as an alternative to PI controller. Moreover, the application of an unprecedented design process based on changing notch filter dynamics with symmetrical pole placement around resonant frequency overcomes the limitations that are essentially complexity and dependency on the precisely modelled system associated with the use of various controllers such as Adaptive, Predictive and Hysteresis in grid connected PV power generation systems. The proposed PR-P controller was validated employing Photovoltaic emulator (PVE) consisting of a DC-DC Buck power converter, a maximum power point tracking (MPPT) algorithm and a full-bridge grid connected inverter designed using MATLAB/Simulink system platform. Details of the proposed controller, Photovoltaic emulator (PVE) simulations, analysis and test results were presented in the paper.

 KEYWORDS:

1.      Proportional resonant current controller

2.      Harmonic compensator

3.      Buck converter based PV emulator

4.      MPPT

SOFTWARE: MATLAB/SIMULINK

CIRCUIT DIAGRAM:

Figure 1. PVE Based Single Phase Grid-Connected Inverter System.

EXPECTED SIMULATION RESULTS:

Figure 2. The PVE Current For Varying Irradiance.

Figure 3. The PVE Voltage For Varying Irradiance.

Figure 4. System Outputs With The Use Of Proposed PR-P Controller.

Figure 5. Generated Power With Delivered And Reactive Powers.

Figure 6. Closed-Loop Error In Terms Of 3^rd Order Harmonics.

Figure 7. PR-P And PI Controlled Grid Currents With Scaled Grid Voltage.

CONCLUSION:

This paper has presented an alternative unprecedented design process for a Proportional-Resonant (PR) controller with a selective harmonic components (3rd and 5th order) compensator for Photovoltaic Emulator (PVE) supported single phase Grid Connected Inverter (GCI) systems. The design procedure of the proposed controller unity proportional resonant (PR) path is conducted based on notch filter dynamics regulated by symmetrical pole placement methods. Addition of scheduled proportional gain designed by loop shaping method to the resonant path increased the performance of the controller in terms of robustness, achieving better results in the presence of non-linear load and weak grid. The performance of the proposed controller and harmonic compensator is validated employing a PVE consisting of a DC-DC Buck converter, a Maximum Power Point Tracking (MPPT) algorithm and a full-bridge GCI designed using MATLAB/Simulink platforms. Frequency and time domain analysis of the system elements showed satisfactory behaviors. A comparative analysis with different PR controller design techniques used in various papers is performed and resulted in confirming that the proposed technique is robust and simple to implement. The performance of the Proposed PR-P controller with the harmonic compensator is compared with a PI in stationary reference frame and conventional PR current controllers in terms of steady-state error and harmonics mitigation. The simulation results demonstrated that the proposed PR-P controller with harmonic compensator is superior at tracking sinusoidal reference current with zero steady-state error and lower total harmonic distortion with eliminated 3rd and 5th order harmonics. The overall system is under development and experimental results will be presented in the near future.

REFERENCES:

[1] R. Ayop and C. W. Tan, ``A comprehensive review on photovoltaic emulator,'' Renew. Sustain. Energy Rev., vol. 80, pp. 430_452, Dec. 2017.

[2] S. Seyam, I. Dincer, and M. Agelin-Chaab, ``Development of a clean power plant integrated with a solar farm for a sustainable community,'' Energy Convers. Manage., vol. 225, Dec. 2020, Art. no. 113434.

[3] W. Xiao, Photovoltaic Power Systems: Modeling, Design, and Control, 1st ed. Hoboken, NJ, USA: Wiley, 2017.

[4] G. Price, Renewable Power and Energy, 1st ed. New York, NY, USA: Momentum Press, 2018.

[5] B. Carrera and K. Kim, ``Comparison analysis of machine learning techniques for photovoltaic prediction using weather sensor data,'' Sensors, vol. 20, no. 11, p. 3129, Jun. 2020.

 

Stability Evaluation of AC/DC Hybrid Microgrids Considering Bidirectional Power Flow Through the Interlinking Converters

ABSTRACT:

 The bidirectional power flow through the interlinking converter (IC), in ac/dc hybrid microgrids (HMGs) consisting of distributed generators (DGs) with droop controllers, plays an important role on the stability of such systems during islanding. This paper investigates the impact of the power flow direction on the small-signal stability of islanded droop-based HMGs. Firstly, a linearized state-space model of an HMG is developed. Secondly, eigenvalue analysis is carried out to realize the dominant modes, which are the rightmost eigenvalues. Thirdly, participation factor analysis is performed to identify the system and control parameters that effect stability the most. Lastly, sensitivity analysis is conducted to determine the critical droop gains and stability margin. It is observed from the eigenvalue and sensitivity analysis that the dominant modes of HMGs become more stable as more power flows from dc to ac subgrid. On the contrary, an increase in the power flow from ac to dc subgrid degrades the HMG stability. Additionally, the sensitivity of the dominant modes to changes in ac and dc droop gains is studied under bidirectional power flow through the IC to ascertain their impact on the stability margins. Finally, time-domain simulations, in MATLAB/Simulink, suggest that more generation on the dc subgrid would enhance the overall HMG stability margin during islanding.

KEYWORDS:

1.      Bidirectional power flow

2.      Distributed generator

3.      Droop controller

4.      Ac/dc hybrid microgrid

SOFTWARE: MATLAB/SIMULINK

CONTROL DIAGRAM:

Figure 1. General Converter-Based Dg Control Structure.

EXPECTED SIMULATION RESULTS:

Figure 2. Dynamic Responses For Dc To Ac Power Flow Condition Without Ic Reactive Power Support.

 

 

Figure 3. Dynamic Responses For Dc To Ac Power Flow Condition With Ic Reactive Power Support.

Figure 4. Dynamic Responses For Ac To Dc Power Flow Condition.

 

Figure 5. Dynamic Responses For An Increase In The Ac Power Generation Capacity.

Figure 6. Dynamic Responses For An Increase In The Dc Power Generation Capacity.

 

 

Figure 7. Dynamic Responses For Ac To Dc Power Flow Condition In Case

Of (Pac 􀀀 V ) And (Qac 􀀀 !) Droop Control In The Ac Subgrid. Figure 16. Dynamic Responses For Ac To Dc Power Flow Condition In Case Of (Pac 􀀀 V ) And (Qac 􀀀 !) Droop Control In The Ac Subgrid.

CONCLUSION:

The operating point including the amount and direction of the power flow between ac and dc subgrids in an HMG largely affects the stability. Thus, this paper investigated the impact of the power flow on the stability of HMGs formed by the interconnection of ac and dc subgrids through bidirectional ICs. It is observed that as the power flow from the ac to dc subgrid increases, the stability margin of the HMG may be reduced. This is mainly because when the power is exchanged from the ac to dc subgrid, the dynamics associated with the ac subgrid have greater influence on the HMG stability as compared to those of the dc subgrid. Moreover, an increase in the generation capacity of the ac subgrid increases the power flow from the ac to dc subgrid to supply the dc load power, which could degrade the stability of the HMG. Thus, it is technically advised to design the HMG such that the ac subgrid receives power from the dc subgrid. The stability analysis presented in this paper is not meant to emphasize that the amount and direction of the power transfer could always jeopardize the stability but rather, precaution should be exercised when transferring power from one subgrid to the other.

 REFERENCES:

[1] S. Anand, B. G. Fernandes, and J. Guerrero, ``Distributed control to ensure proportional load sharing and improve voltage regulation in low- voltage DC microgrids,'' IEEE Trans. Power Electron., vol. 28, no. 4, pp. 1900_1913, Apr. 2013.

[2] R. Majumder, ``Some aspects of stability in microgrids,'' IEEE Trans. Power Syst., vol. 28, no. 3, pp. 3243_3252, Aug. 2013.

[3] E. A. A. Coelho, P. C. Cortizo, and P. F. D. Garcia, ``Small-signal stability for parallel-connected inverters in stand-alone AC supply systems,'' IEEE Trans. Ind. Appl., vol. 38, no. 2, pp. 533_542, Aug. 2002.

[4] F. Gao, S. Bozhko, A. Costabeber, C. Patel, P. Wheeler, C. I. Hill, and G. Asher, ``Comparative stability analysis of droop control approaches in voltage-source-converter-based DC microgrids,'' IEEE Trans. Power Electron., vol. 32, no. 3, pp. 2395_2415, Mar. 2017.

[5] J. M. Guerrero, L. GarciadeVicuna, J. Matas, M. Castilla, and J. Miret, ``A wireless controller to enhance dynamic performance of parallel invert- ers in distributed generation systems,'' IEEE Trans. Power Electron., vol. 19, no. 5, pp. 1205_1213, Sep. 2004.

Solar Powered Unmanned Aerial Vehicle With Active Output Filter Under Non-Linear Load Conditions

ABSTRACT:

This paper presents a new electric power train for solar powered unmanned aerial vehicle (UAV). The proposed system structure is based on the development of the power supply system for both the So long and Zyphyr aircraft models. The proposed UAV model incorporates the Zyphry UAV use of an AC line feeder instead of DC power lines to power the propellers. The proposed power train includes solar panels, an energy management system based on lithium sulfide battery, inverter, AC bus-line and active output filter (AOF). AOF topology is composed of a high switching frequency H-bridge inverter with a reduced size LC filter. The utilization of AOF system reduces the size and weight of the power transmission system and significantly improves its conversion efficiency by introducing an emulated series resistance with the H-bridge stage to ensure high quality pure sinusoidal waveform of the line voltage. This emulated series resistance produces an injected voltage across it to diminish unwanted harmonics created from the non-linear load. A simulation model and experimental setup are created to simulate the proposed system and the system is tested under non-linear load condition with closed-loop feed-back control strategy. The obtained simulation and experimental results demonstrate that high-quality sinusoidal line voltage waveforms can be obtained using the active resistance compensation technique with total harmonic distortion factor less than 3%. Moreover, power losses analysis and conversion efficiency calculation of the proposed system are performed and compared with that of the conventional three-phase PWM inverter, which proved that the power losses are reduced by 31%.

KEYWORDS:

1.      Active output filter

2.      Active resistance compensation

3.      Loss analysis

4.       Non-linear load

5.       Solar powered

6.      Unmanned aerial vehicle

 SOFTWARE: MATLAB/SIMULINK

CIRCUIT DIAGRAM:

Figure 1. Proposed Solar Powered Uav And Aof, (A) Single-Phase Square Wave Inverter With Ac-Bus Line And (B) Three-Phase Six-Step Inverter With Ac-Bus Line.

 EXPECTED SIMULATION RESULTS:

Figure 2. Tested Insolation Conditions For Uav Pv Power System.

 

Figure 3. Pv Harvested Power.

 

Figure 4. Pv Voltage (Upper Trace) And Current (Low Trace).

 

Figure 5. Battery Power.

 

Figure 6. Non-Linear Load Output Dc Power.

Figure 7. Pv Harvested Power During Different Operating Modes.

 

CONCLUSION:

A new electric power generation system for solar powered unmanned aerial vehicle (UAV) using active output filter has been proposed and investigated in this paper. The proposed power generation system is a potential progress of both the Solong and Zyphyr UAV models using the AC-bus line instead of the DC-bus line to power the propellers. It includes solar PV system, lithium-sulfur based power management system, inverter, AC bus-line. Balanced DC-link voltages of AOF have been accomplished using closed loop control of active resistance compensation, which produces an injected voltage across it to diminish unwanted harmonics created from the non-linear load. The obtained simulation and experimental results and the voltage and current waveforms demonstrated the viability and the correctness of the proposed power generation system. The proposed active resistance compensation ensures a high-quality sinusoidal line voltage with total harmonic distortion less than 3%. Moreover, power loss analysis and conversion efficiency of the proposed system are performed and compared with that of the conventional three-phase PWM inverter. The obtained results proved that the power loss is reduced by 31%. More investigation of the proposed AOF for large-scale PV plants application with Battery energy management system integration using different wide band gab devices to optimize the system efficiency are required with applying different PWM techniques to utilize the passive elements sizing design which are the subject of future work.

REFERENCES:

[1] U. Burup, P. N. Enjeti, and F. Blaabjerg, ``Anewspace-vector-based control method for UPS systems powering nonlinear and unbalanced loads,'' IEEE Trans. Ind. Appl., vol. 37, no. 6, pp. 1864_1870, Nov./Dec. 2001, doi: 10.1109/28.968202.

[2] D. Zhang, J. He, and D. Pan, ``A megawatt-scale medium-voltage high efficiency high power density `SiCCSi' hybrid three-level ANPC inverter for aircraft hybrid-electric propulsion systems,'' IEEE Trans. Ind. Appl., vol. 55, no. 6, pp. 5971_5980, Nov. 2019, doi: 10.1109/TIA.2019.2933513.

[3] M. N. Boukoberine, Z. Zhou, and M. Benbouzid, ``A critical review on unmanned aerial vehicles power supply and energy management: Solutions, strategies, and prospects,'' Appl. Energy, vol. 255, no. 1, pp. 1_22, Dec. 2019, doi: 10.1016/j.apenergy.2019.113823.

[4] X. Zhao, J. M. Guerrero, and X. Wu, ``Review of aircraft electric power systems and architectures,'' in Proc. IEEE Int. Energy Conf. (ENERGY- CON), Cavtat, Croatia, May 2014, pp. 949_953, doi: 10.1109/ENERGYCON. 2014.6850540.

[5] O. D. Dantsker, S. Imtiaz, and M. Caccamo, ``Electric propulsion system optimization for long-endurance and solar-powered unmanned aircraft,'' in Proc. AIAA Propuls. Energy Forum (EATS), Indianapolis, IN, USA, Aug. 2019, pp. 1_24, doi: 10.2514/6.2019-4486.

 

Small Signal Stability Analysis Oriented Design of Hybrid Anti-Islanding Protection Technique Based on Active Disturbance Injection

ABSTRACT:

 The conventional over/under voltage, over/under frequency based anti-islanding protection scheme presents significant nondetection zone (NDZ) under critical loading conditions of distribution networks. To overcome this challenge, a unique hybrid technique has been proposed in this article for the anti-islanding protection of distributed generators (DGs). The algorithm requires the injection of an active oscillatory disturbance signal of very small magnitude through the current control loop along the direct axis of the synchronously rotating reference frame of the converter. Small signal stability analysis of the system is carried out to analyze the effect of such active signal injection having different frequencies. The anti-islanding protection algorithm first involves the superimposition of d-axis voltage. Thereafter, two novel indexes are proposed based on which the trip signal logic is developed for the protection scheme. The methodology has been found to detect an unintentional islanding scenario within 90 ms from the initiation instant. The efficacy of the proposed hybrid anti-islanding protection scheme is tested under various abnormal operating conditions by performing simulations on the CIGRE LVtest system. Experimental validation of the proposed methodology has also been carried out in Controller Hardware-in-the-Loop (CHIL) platform using Typhoon HIL 602+ and Speedgoat baseline real-time target machine.

KEYWORDS:

1.      Active disturbance injection

2.      Anti-islanding protection

3.      Distributed generators (DGs)

4.       Small signal stability

5.      Superimposition

SOFTWARE: MATLAB/SIMULINK

CONTROL DIAGRAM:

Fig. 1. Control strategy adopted for the DGs with signal injection through direct axis current control loop.

 EXPECTED SIMULATION RESULTS:

Fig. 2. Performance of the proposed scheme under zero power mismatch condition.

Fig. 3. Performance of the proposed scheme under different types of load Switching

Fig. 4. Performance of the proposed scheme under unbalanced loading condition

 

CONCLUSION:

Small signal stability analysis-oriented design of a hybrid real-time anti-islanding protection scheme has been proposed and successfully demonstrated in this article. The prominent features of the proposed method can be listed as follows.

1) Faster detection time of an unintentional islanding event compared to most of the proposed methods in literature even under the worst case scenario.

2) The selection of amplitude of the disturbance signal has been done considering the negative impact on power quality. On the other hand, the frequency of the active disturbance signal has been selected in such a way that it avoids any kind of excitation of the modes of the system thereby causing instability.

3) Due to the superimposition of the d-axis voltage, the effects due to transients are nullified and the methodology preserves both security and dependability attribute.

4) Although the theoretical analysis has been carried out in the standard IEEE 1547 test system, the protection technique proposed in this article is generalized and can be applied for DGs in any distribution networks.

The efficacy of the proposed algorithm is evaluated under various operating conditions by conducting simulations on the CIGRE LV distribution network. Further, the real-time performance evaluation of the proposed algorithm has been carried out in the CHIL platform using Typhoon HIL 602+ and Speed goat baseline real-time target machine on standard IEEE 1547 test system under various operating conditions. It has been observed that the algorithm is robust under different operating scenarios and is able to preserve its desired functionality in most of the cases.

REFERENCES:

[1] F. Blaabjerg, Y. Yang, D. Yang, and X. Wang, “Distributed power generation systems and protection,” Proc. IEEE, vol. 105, no. 7, pp. 1311–1331, Jul. 2017.

[2] UL Standard for Safety for Inverters, Converters, Controllers, and Interconnection System Equipment for Use with Distributed Energy Resources, UL 1741, 2010.

[3] “Standard for interconnecting distributed resources with electric power systems,” in Proc. IEEE Std. 1547, 2003, pp. 1–28.

[4] F. Noor, R. Arumugam, and M. Y. Vaziri, “Unintentional islanding and comparison of prevention techniques,” in Proc. 37th Annu. North Amer. Power Symp., 2005, pp. 90–96.

[5] S. Dutta et al., “Shifting of research trends in islanding detection method— A comprehensive survey,” Protection Control Modern Power Syst., vol. 3, pp. 1–20, 2018.

Robust Control for Islanded and Seamless Mode Switching of Wind-PV-Grid Tied Generation System

  ABSTRACT:

 This paper deals with robust control strategy for a distributed generation system (DGS), which operates in both islanded and grid-connected modes. Generally, in the low-voltage islanded mode of DGS, the PCC (Point of Common Coupling) voltages are unbalanced due to the unbalanced load connection. Therefore, in an islanded mode of DGS, the LSC is controlled using the IPR (Improved Proportional Resonant) controller to maintain the PCC voltages quality within the IEEE-1547 standard. Moreover, the DGS is capable to synchronize to the grid without any transient current. During the change of modes of DGS, large transients occur in the battery current due to the switching of battery control. This problem is resolved by the presented bidirectional DC-DC converter control strategy and robust ILQSOGI (Inner Loop Quadrature Second Order Generalized Integrator) based PLL. The effectiveness of this DGS control strategy is verified by the corresponding MATLAB/Simulink platform under load unbalance, solar irradiance changes and during mode of switching. Moreover, the simulation results are validated using the test results and show the robustness of the control strategy during abnormal grid voltage condition.

KEYWORDS:

1.      Solar Photovoltaic Array

2.      Power Quality

3.      Bidirectional DC-DC Converter

4.      Load Side Converter (LSC) and Machine Side Converter (MSC)

SOFTWARE: MATLAB/SIMULINK

SCHEMATIC DIAGRAM:

Fig.1 Proposed DGS configuration

EXPECTED SIMULATION RESULTS:

Fig. 2 Performance of DGS during mode of switching from IMS to GCM

 

Fig. 3 Power quality indices of DGS in GCM (a) harmonic spectrum of ig (b) harmonic spectrum of iL

Fig. 4 Performance of BDC control under mode of transition (a) without and with BDC control under grid connection (b) without and with BDC control under grid disconnection.

 

Fig. 5 Comparison of load voltage waveforms (a) with proposed islanded control technique (b) conventional islanded PI control techniq

Fig. 6 Comparison of load voltage THD (a) with proposed islanded control technique (b) conventional islanded PI control technique

 

Fig. 7 Performance of DGS (a) solar and wind power variation in IMS (b) at unbalanced load condition in IS mode

CONCLUSION:

The proposed islanded control technique has used the positive sequence load current components with PR control, which has improved the load voltage quality under unbalanced nonlinear load condition and the results have proven the robustness of control technique in islanded mode of DGS. Simulated results have shown the significant difference in PCC load voltage quality using conventional and proposed islanded control technique. Moreover, simulated results have proven the good load voltage quality under unbalanced nonlinear load condition and the range of load voltage quality lies under the IEEE-1547.4 standard. Experimental results show the robustness of the control strategy, which is capable to operate the DGS in different modes such as in grid connected mode and islanded mode. Moreover, the transient free mode change is also presented through test results. The qualities of PCC voltages and currents are also maintained under the IEEE-1547 standard, in the grid connected mode, an islanded mode and during mode transitions. Test results have presented the performance of DGS under different dynamic conditions and validated the robustness and effectiveness of control schemes. Test results have also shown the effectiveness of feed-forward term in grid connected mode and the smooth operation of grid connected mode under battery disconnection.

REFERENCES:

[1] B. Zeng, J. Zhang, X. Yang, J. Wang, J. Dong and Y. Zhang, “Integrated Planning for Transition to Low-Carbon Distribution System with Renewable Energy Generation and Demand Response,” IEEE Trans. Power Systems, vol. 29, no. 3, pp. 1153-1165, 2014.

[2] M. Savaghebi, A. Jalilian, J. C. Vasquez and J. M. Guerrero, “Secondary Control Scheme for Voltage Unbalance Compensation in an Islanded Droop-Controlled Microgrid,” IEEE Trans. Smart Grid, vol. 3, no. 2, pp. 797-807, June 2012.

[3] IEEE Guide for Design, Operation, and Integration of Distributed Resource Island Systems with Electric Power Systems, IEEE Standard

[4] Bhutto, Ghullam and Bak, C.L. and Ali, Ehsan, “Controlled Operation of the Islanded Portion of the International Council on Large Electric Systems (CIGRE) Low Voltage Dist. Network”, Energies, 20.17.

[5] M. E. Baran and F. F. Wu, “Network reconfiguration in distribution systems for loss reduction and load balancing,” IEEE Trans. Power Delivery, vol. 4, no. 2, pp. 1401-1407, April 1989.